Gnumeric

The Gnumeric spreadsheet is intended to be a drop in replacement for proprietary spreadsheets. We are not attempting to clone existing applications. However, we offer a customizable feel that attempts to minimize the costs of transition.
Gnumeric will import your existing Excel, 1-2-3, Applix, Sylk, XBase Quattro Pro, Dif, Plan Perfect, and Oleo files. If you are a developer and you want to contribute new importers (or polishing and perfect existing importers) we welcome your patches. We are also looking for test cases for the various formats, non coders who can produce comprehensive sample workbooks so that we can validate the importers would also be appreciated.